M7010R datasheet(22/67 Pages) STMICROELECTRONICS

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M7010R

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SEARCH PROCEDURE FOR 32-BIT WIDE PREFIXES

The Global Mask Register is used for 32-bit wide

data paths as follows:

Writing a '1' in the Global Mask Register allows

data to be written into the M7010R. A '0' in the Glo-

bal Mask Register disallows data modification. In-

formation is written into the left half of the 68-bit

word Search Engine as long as space for 34 bits

of data is available and then into the right half of

the Search Engine. 32-bit data can be entered in

two cycles.

The first step is to write into two of the eight Global

Mask Registers with the patterns shown in Figure

15. Writing this data using Global Mask Register 1

allows the left half of the data array to be com-

pletely filled.

Figure 16 shows Bits 67 through 36 in the left sec-

tion of the data array representing 32-bits of data.

Bits 35 and 34 shown separately can be defined

by the user for table management. In this applica-

tion 34-bit operation occurs in each half-section of

the Data and Mask arrays of the Search Engine.

The left half is filled first, then the right. Not all lo-

cations have to be filled.

SEARCH operations are performed twice, once on

the left half and then on the right half. Note that a

'1' in the Global Mask register enables a compare

during a SEARCH operation and a '0' forces a

match condition regardless of the state of the data

bit.

The SEARCH throughput for 34-bit operations is

half of the 68-bit operations. A search is performed

by using the Global Mask Register “0” for the left

half of the 68-bit, then another search is performed

using Global Mask Register 1 for the right half of

the 68-bit word. The order is important, as the left

half has a higher priority than the right half.

For example, if a search on the left half produces

a match and a search on the right half also produc-

es a match, then in that case, the left half is a high-

er priority. So if only one unique match exists in a

particular system, then a match on the left side

may alleviate the need to do a search on the right

half of the Data array.

Figure 15. Global Mask Register Patterns

Figure 16. Storing left half of a Data or Mask

Array

111

1000

000

0111

Bits

3433

AI04277

Bits

36 35

1 0

AI04278

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